The relationship between coal workers' pneumoconiosis (CWP) and dust exposure in US coal miners was examined using data obtained between 1969 and 1971 from the National Study of CWP. Relationships between the prevalence of category one and two CWP and progressive massive fibrosis (PMF) and coal dust exposures, coal rank, and age of the miners were examined using log likelihood and logistic techniques. Category prevalence increased significantly with coal dust exposure across all coal ranks. The prevalence of PMF was significantly associated with dust exposure for the three highest ranked coals, coals that contained 80 to 93% carbon. Age was strongly associated with CWP, even after adjusting for years of underground mining and dust exposure. The predicted prevalences of category one and category two CWP and PMF for a lifetime exposure bituminous mines to coal dust at the current federal standard, 2mg/m3, were 8.2 to 28.2, 1.5 to 11.5, and 1.3 to 6.5%, respectively. Prevalences for 40 years exposure to 2mg/m3 dust in anthracite mines were 31.7, 14.2, and 8.9%, respectively. The authors conclude that these prevalences can be correlated with exposure to coal mine dust. Predicted prevalences of CWP for miners exposed at the level of the 2mg/m3 standard are greater than originally expected when the standard was enacted. The risk may be higher for miners who work in mines where high rank coal is mined. The predicted CWP prevalences are similar to but higher than those obtained in recent studies of British coal miners.